A mother lost two babies to Leigh syndrome, a fatal genetic disorder, and experienced a slew of miscarriages. To help her carry a healthy baby, scientists in Mexico used a new technique that involves taking the nucleus from one of the mother’s eggs and implanting it into a donor egg with the nucleus removed but containing the healthy mitochondrial DNA.

This technique is intended to help parents avoid passing on mitochondrial diseases, which afflict 1,000 to 4,000 people in the U.S. each year.

Versions of this technique are banned in the U.S., but in Mexico, there are comparatively few rules. Some critics say it allows scientists to play God. But many in the scientific community are urging regulators to reconsider their stance. The ban is “not scientific, not rational, not evidence-based,” Dr. Richard J. Paulson, president-elect of the American Society for Reproductive Medicine told the New York Times. CF